DEVELOPMENT OF AN ULTRA-HIGH TEMPERATURE PYROLYTIC GRAPHITE THERMOCOUPLE.
Final rept., 1 Jan-30 June 63,
RAYTHEON CO WALTHAM MASS
Pagination or Media Count:
Electrical and galvanomagnetic effects along the layer planes of three classes of pyrolytic graphites heat-treated, as-deposited, and borondoped are investigated in the temperature range from 0 to 1000 C. It is shown that the simple two-band model with symmetrical upper and lower pi bands and zero-gap configuration provides an adequate description of the charge-transport mechanism. Carrier concentrations and mobilities substantiate previous conclusions derived from low-temperature work, and allow us to assess crystallite sizes on an independent basis. Theoretical evaluations of the Seebeck coefficient are performed in the framework of a formation presumed rigorous for semimetals. Critical information on the scattering parameter of pyrolytic graphite is thus deduced. Experimental Seebeck-coefficient results confirm the main features of the analysis, in particular the type reversal that occurs in turbostratic graphites at temperatures of about 500 C. Thermocoupledesign feasibility studies reveal that PGBPG systems are capable of operation at least up to 2800 C. Author